Perfluoroelastomers have achieved outstanding commercial success and are used in a wide variety of applications in which severe environments are encountered, in particular those end uses where exposure to high temperatures and aggressive chemicals occurs. For example, these polymers are often used in seals for aircraft engines, in oil-well drilling devices, and in sealing elements for industrial equipment used at high temperatures.
The outstanding properties of perfluoroelastomers are largely attributable to the stability and inertness of the copolymerized perfluorinated monomer units that make up the major portion of the polymer backbones in these compositions. Such monomers include tetrafluoroethylene and perfluorinated vinyl ethers. In order to develop elastomeric properties fully, perfluoroelastomers are typically crosslinked, i.e. vulcanized. To this end, a small amount of cure site monomer is copolymerized with the perfluorinated monomer units. Cure site monomers containing at least one nitrile group, for example perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, are especially preferred. Such compositions are described in U.S. Pat. Nos. 4,281,092; 4,394,489; 5,789,489; and 5,789,509.
U.S. Pat. No. 3,484,503 discloses single phase blends of an elastomeric copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) with a thermoplastic copolymer of tetrafluoroethylene. The elastomeric component does not contain a cure site and so the composition cannot be crosslinked. Seals made from such compositions have relatively poor sealing properties due to the lack of crosslinks.
U.S. Pat. No. 4,713,418 discloses curable perfluoroelastomer compositions which contain a melt blend of perfluoroelastomer and from 2 to 50 parts by weight of a thermoplastic perfluoropolymer. Typically, the thermoplastic polymer has a melting point of at least 300° C. Due to the relatively small loading of thermoplastic perfluoropolymer, seals prepared from these compositions lack the physical strength required for high pressure sealing applications
U.S. Pat. No. 6,710,132 B2 discloses latex blends of a perfluoroelastomer with 2-90 weight percent of a semi-crystalline core/shell fluoroplastic wherein the shell polymer contains bromine and/or iodine in the polymer chain. WO 02/79280 discloses curable latex blends of perfluoroelastomer and fluororesin, wherein the fluororesin has a melting point between 230° and 300° C. and an average particle size of less than 100 nm. Latex blends are not simple or cost effective to make on a commercial scale.
It would be desirable to have a perfluoroelastomer composition which, when crosslinked, provides the combination of good sealing properties, sufficient strength for use in high pressure applications, good chemical resistance and wherein the composition may be made in conventional rubber processing equipment.